The invention relates to the rotating electrical machines which have at least two coaxial armatures separated by an air gap, a stationary stator and a rotor given a uniform movement.
Essentially, multiphase and multipole AC generators concern us here.
These armatures can be cylindrical, and the machine then creates a radial field. The conductors are placed in slots distributed on the internal periphery of the stator or the external periphery of the rotor. The conductors are parallel to the axis of rotation of the machine.
These armatures can also take on the form of a disk, and in this case, the machine creates an axial field. The conductors are placed in radial slots; they are therefore perpendicular to the axis of rotation of the machine.
Conventionally, the conductors are arranged in the slots of a magnetic circuit based on different winding types chosen as a function of the application.
The windings are produced using coils or bars.
The coils are produced using conductors which are insulated from one another and wound in concentric turns. Each coil is placed in two different slots of the magnetic circuit. The two parts of the coil situated in the slots are generally called bundles, and the part of the coil which is outside of the magnetic circuit is generally called the end winding.
Bars are conductors which are not closed on themselves and can be made up of several flattened elements in parallel. The parts situated in the slots are also called bundles. Connections are provided between the bars.
We distinguish principally the windings with concentric sections or the windings with crisscross sections or bars.
The windings with concentric sections or coils can be produced by winding with alternating poles or with consecutive poles.
The conductors are placed in a single slot plane which is composed of two layers produced successively for a winding with consecutive poles, and for a winding with alternating poles, the same number of layers as the number of phases.
These windings have the advantage of being produced in tiers; their prouduction can therefore be easily automated.
However, they have limits and disadvantages.
The windings in one plane are today essentially intended for low power machines for which the cost of manufacturing is preponderant in view of their technical performance. In this case, the conductors are made of round wires with a slot filling which is less than that which can be obtained with flattened conductors, and the winding pitch is a whole number, to the detriment of the behavior of the rotating field.
However, it is possible to produce this type of winding with coils of different geometry using flattened conductors which, because of the differences in bulk of the end windings, can lead to imbalances between phases and to magnetic leakage.
In order to improve the progressiveness of the rotating magnetic field, the production of windings with a shortened pitch is feasible, but its possibilities are limited and it leads to winding assymmetries.
The windings with crisscrossing sections or bars can be produced in the form of a mantle, overlapping or undulating.
These windings allow shortened pitches, and, consequently, they make possible the elimination of certain electrical harmonics.
The most common windings are the overlapping and the undulating which are generally used for machines of medium and high power.
For these applications, the windings are produced manually, from bars in the case of the undulating type, and from bars or coils in the case of the overlapping type.
We are most concerned with the overlapping windings in which the conductors are arranged in the slots in two different planes separated by insulating materials.
These windings have numerous advantages from an electrical standpoint. In particular, they offer great flexibility to the designer of the electrical machine in producing fractional pitches.
Conventionally, a coil is produced by winding rectangular conductors, insulated beforehand, in a winding tower to obtain one or more concentric turns.
The coil generally has the shape of a shuttle which is then stretched in order to open the coil and raise the end winding.
The spacing between the two large sides of a coil that is intended to be placed in slots of a magnetic circuit is a function of the number of poles. The two large sides of the coil are in planes which are offset with respect to one another; these two sides are therefore also situated in different planes of the slots when the coil is placed in the magnetic circuit. This allows one to produce the electrical circuit of the machine by arranging the coils one after another in the magnetic circuit.
An overlapping winding produced from coils has a major disadvantage.
The positioning of all the coils requires raising of the coils arranged first in order to be able to insert the last coils. This operation, ordinarily called pitch raising, is an essentially manual operation, which makes any automation difficult.
It has therefore appeared necessary to propose another type of winding, intended for the magnetic circuit of an electrical machine, which is easily automated and which has the same electrical advantages as an overlapping-type winding.
The invention relates, therefore, to a process for production of a winding for the magnetic circuit of a rotating electrical machine in which the conductors are placed in the slots of the magnetic circuit in two slot planes, the process comprising producing the two planes of conductors successively and independently, each plane of conductors having at least one layer of conductors.
Inasmuch as at least one plane of conductors has at least two layers of conductors, they are produced successively and independently in such a way that the conductors of each layer are situated in the same plane of the magnetic circuit.
Advantageously, the layers of a plane of conductors are formed by coils, each of them having two bundles and two end windings whose thickness is equal to a fraction of the thickness of the bundles, the coils being symmetrical with respect to the median plane of the bundles.
Preferably, the two planes of conductors are identical.
In order to obtain a winding whose electrical performances are similar to those of an overlapping-type winding, an offset by a determined number of slots is provided between the two planes of conductors.
It is advantageous to produce each of the electrical circuits of a determined phase continuously to avoid any later connection between the conductors.
Preferably, the coils are formed directly in the slots of the magnetic circuit.
Furthermore, the process can be implemented with consecutive or alternating poles.
The invention also relates to a winding produced by the preceding process for a three-phase electrical machine, the assignment of the phases to each conductor being identical to that of a corresponding overlapping-type winding, with the exception of a phase inversion from one slot plane to the other as a function of the pitch in certain defined slots.
For a winding of the type with a pitch of 1 to 4, the phase inversion is produced for every other slot.